I would recommend TR1879 which leaves Cambridge at 13:06 and arrives in Peterbourough at 13:56.
I'm sorry, I had that backwards, I need a train that departs FROM Peterborough and goes to Cambridge.
train-day train-departure train-destination train-leaveat
train-day train-departure train-destination train-leaveat
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train-day train-departure train-destination train-leaveat